x–4/9–5/9–z=2/3
解: x-z= 2/3+5/9 +4/9 x-z =5/3 x=5/3+3或z=x-5/3
解: x-1-z=2/3
x-z=5/3
x=5/3+z
(x-2/3)-(z+1)=0
x=2/3
z=-1